Question

A Uniform magnetic field is obtained in
A. A bar magnet
B. A horseshoe magnet
C. A circular coil carrying current
D. A cylindrical coil carrying current

Answer 1

Hint: A uniform magnetic field is a magnetic field that has the same strength and direction at all points. It is denoted by a set of parallel lines that are equally spaced apart. The direction of the magnetic field lines is in the same direction as the magnetic field lines of a magnet.

Complete step by step solution:
A uniform magnetic field has parallel magnetic field lines and has the same strength and direction at all points which means the magnetic force experienced by an object is the same at all points.
In the case of a bar magnet,
A bar magnet produces a non-uniform magnetic field that can be seen by the magnetic lines of force arising from the north pole of the magnet and progressing towards the south pole of the magnet. For a non-uniform magnetic field, the magnetic field lines are not equally spaced and parallel, but are either converging or diverging.
In the case of a horseshoe magnet,
A horseshoe magnet produces a non-uniform magnetic field as it does not have the same strength at all points and the field lines are neither equally spaced nor parallel.
In the case of a circular current-carrying coil,
When current is passed through a circular coil or loop, the magnetic field is generated around the coil. The magnetic field produced due to a current-carrying circular coil is not a uniform magnetic field as it does not have the same strength at all points and the field lines are neither equally spaced nor parallel. Though, it can be considered uniform at the center of the coil.
In the case of a cylindrical current-carrying coil,
A uniform magnetic field can exist in a comparatively long cylindrical coil. Once current starts flowing through the coil a uniform magnetic field will be generated and will exist all along with the interior of the coil.
Hence, we can say that a uniform magnetic field can be obtained from a current-carrying cylindrical coil.
Therefore, option (D) A cylindrical coil carrying current is the correct option.

Note:
The magnetic field generated by a cylindrical current-carrying coil is not perfectly uniform because a uniform magnetic field is not valid at the ends of the cylindrical current-carrying coil. Still, it principally produces a uniform magnetic field inside the cylindrical current-carrying coil.